The subject matter of this disclosure is directed generally towards a wireless communications network for determining whether a signal from a mobile appliance is operated by a repeater or other network device.
The use of wireless communication devices such as telephones, pagers, personal digital assistants, laptop computers, etc., hereinafter referred to collectively as “mobile appliances,” have become prevalent in today's society.
FIG. 1 shows a conventional mobile-appliance communication system having base stations 10 a-c for communicating with a mobile appliance 20. Each base station 10 contains signal processing equipment and an antenna for transmitting to and receiving signals from the mobile appliance 20 as well as other base stations. A Base Station Controller (“BSC”) and/or Mobile Switching Center (“MSC”) 45 typically is connected to each base station 10 through a wire line connection 41.
To meet the ever growing demand for mobile communication, wireless communication systems deploy repeater stations to expand range and concentration of coverage. In FIG. 1, a repeater 50a, associated with base station 10a, is located to extend the coverage area to encompass the back side of the mountain 1. The repeater 50b, associated with base station 10c, is mounted on a building and is used to provide service within the building 2.
Repeaters typically fall into two categories: (1) non-translating, also known as wideband, and (2) translating, also known as narrowband. As shown in FIG. 2a, a non-translating repeater 250 simply passes the forward Ff1 and reverse Rf1 frequencies from the base station 210 and mobile appliance 220 respectively to and from the repeater coverage location. Often wideband repeaters are “in-building” or serve limited coverage areas. While the description of non-translating repeaters above and translating repeaters below are described in reference to frequency, their operation can equally be described in terms of channels, and the use of the term frequency should not be construed to limit the scope of the present disclosed subject matter.
A translating repeater assigns the mobile to a different traffic channel unbeknownst to the base station, mobile switch, MPC, and the base station controller. As shown in FIG. 2b, the translating repeater uses the base station traffic channel Rf1 for repeater 250 to base station 210 communication while the mobile appliance 220 utilizes a separate frequency Rf2 for mobile to repeater communications. Translating repeaters act similarly in the forward direction using Ff1 from the base station 210 to the repeater station 250 and Ff2 from the repeater station 250 to the mobile appliance 220. In both cases, the existence of the repeater is usually transparent to the network.
The function of the repeater station can be assumed to be equivalent to converting all signals in some received bandwidth from a Radio Frequency (RF) to some Intermediate Frequency (IF). The IF signal bandwidth is then up-converted by suitably frequency shifting this bandwidth while concurrently applying both amplification and a fixed delay to the signals.
For example, let the set of signals transmitted by N mobiles in the repeaters' input bandwidth be denoted by
            S      ⁡              (        t        )              =                  ∑                  k          =          1                N            ⁢                        a          ⁡                      (            k            )                          ⁢                  x          ⁡                      (                          k              ,              t                        )                          ⁢                  sin          ⁡                      (                          w              ⁢                                                          ⁢              t                        )                                ,where the signal from a given mobile is denoted by x(k, t). The signal x(k, t) is contained in the repeater bandwidth and w is the angular frequency center of the RF bandwidth. The repeater downshifts the aggregate signal to generate
            D      ⁡              (        t        )              =                  ∑                  k          =          1                N            ⁢                        a          ⁡                      (            k            )                          ⁢                  x          ⁡                      (                          k              ,              t                        )                          ⁢                  sin          ⁡                      (            vt            )                                ,in which v is now representative of the center of the IF bandwidth. The entire signal D(t) is now converted back to RF by operations that are equivalent to forming the signal
            R      ⁡              (                  t          +          T                )              =                  G        ⁢                              ∑                          k              =              1                        N                    ⁢                                    a              ⁡                              (                k                )                                      ⁢                          x              ⁡                              (                                  k                  ,                  t                                )                                      ⁢                          sin              ⁡                              (                                  v                  ⁢                                                                          ⁢                  t                                )                                      ⁢                          cos              ⁡                              (                                                      w                    ⁢                                                                                  ⁢                    t                                    -                                      v                    ⁢                                                                                  ⁢                    t                                                  )                                                        +              G        ⁢                              ∑                          k              =              1                        N                    ⁢                                    a              ⁡                              (                k                )                                      ⁢                          x              ⁡                              (                                  k                  ,                  t                                )                                      ⁢                          cos              ⁡                              (                                  v                  ⁢                                                                          ⁢                  t                                )                                      ⁢                          sin              ⁡                              (                                                      w                    ⁢                                                                                  ⁢                    t                                    -                                      v                    ⁢                                                                                  ⁢                    t                                                  )                                                          ,in which G is the repeater gain. The last equation can be written in a more convenient, mathematical manner by noting that R(t) can be derived from D(t) by writing it as R(t+T)=Re{G exp(j(w−v)tI/(t))}, where G exp(j(w−v)t) is the complex representation of the multiplicative signal introduced by the repeater on the downshifted signal bandwidth and I(t) is the complex representation of D(t).
Essentially, the function of the repeater is to convert the RF signal to an IF signal, delay and amplify that IF signal, up-convert the signal back to RF, and transmit the signal. This is true for both translating and non-translating repeaters.
Repeaters typically communicate with the host base station via an RF link as shown in FIG. 3 between base station 310 and repeater 350a. This connection allows remote operation of the repeater without physical ties back to the host base station, which is particularly advantageous in rugged or other areas where laying lines are difficult or costly. Some repeaters, generally non-translating repeaters, use a fiber optic or copper wire “tether” instead of an RF link to communicate with the host base station as shown in FIG. 3, where base station 310 is connected to repeater station 350b by tether 351. RF signals are placed onto the tether at the repeater and then summed into the normal base station antenna path at the antenna feed interface 311 at the host base station. After integration into the normal base station antenna path, the signal from the repeater is indistinguishable to the base station regarding its origin (e.g., from the base station antennas or from a tether). In this tether architecture as well, the host base station has no knowledge of the repeater's existence or that a call is being served by the repeater.
Neither the base station nor the switch knows that a repeater or other network device is serving a call. For example, a repeater installed as an in-building distribution system would use indoor antennas to communicate with the indoor handsets and an outdoor antenna to communicate with the host base station.
Repeaters are often not equipped with GPS modules as are location measurement units as such the reference clock of the repeater is subject to drift. This drift is detrimental to detection of the uplink signal.
Repeaters are also generally not aware of the mobiles which they are servicing as described above they repeat any signal received within its domain band.
In order to accomplish location determination in an environment with repeaters, there is a need to overcome the deficiencies in the prior art by employing a novel system and method that is capable of identifying when a mobile's signal is being received via a repeater or other network device by determining its proximity to the repeater. In view of this need, it is an object of the disclosed subject matter to present a method for determining whether a signal is received directly from the mobile or from a repeater in the communication network.
It is also an object of the disclosed subject matter to provide a method by which repeaters may actively assist in determining mobiles in its proximity and thus those mobiles likely served.
The ability to discern the difference between direct signals and repeated signals (i.e., signals that arrive via a repeater) allows for the system to be better managed and is thus advantageous.
These objects and other advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.